1. Technical Field
This disclosure relates to the use of focused ion-beam (FIB) microscopes for the preparation of specimens for later analysis in the transmission electron microscope (TEM), and apparatus and methods to facilitate these activities.
2. Background Art
The use of focused ion-beam (FIB) microscopes has become common for the preparation of specimens for later analysis in the transmission electron microscope (TEM). The structural artifacts, and even some structural layers, in the device region and interconnect stack of current integrated-circuit devices can be too small to be reliably detected with the secondary electron imaging in a Scanning Electron Microscope (SEM), or FIB, which offers a bulk surface imaging resolution of approximately 3 mm. In comparison, TEM inspection offers much finer image resolution (<0.1 nm), but requires electron-transparent (<100 nm thick) sections of the sample mounted on 3 mm diameter grid disks.
Techniques were later developed for cutting out and removing specimens for examination that required little or no preliminary mechanical preparation of the initial semiconductor die sample before preparation in the FIB. These lift-out techniques include an “ex-situ” method that is performed outside the FIB chamber, and “in-situ” methods performed inside the FIB.
The conventional process of in-situ lift-out can be simplified into three successive steps. The first is the excision of the sample using focused ion-beam milling and extraction of the sample from its trench. The second is the “holder-attach” step, during which the sample is translated on the probe-tip point to the TEM sample holder. Then it is attached to the TEM sample holder (typically with ion beam-induced metal deposition) and later detached from the probe-tip point. The third and final step is the thinning of the sample into an electron-transparent thin section using focused ion beam milling.
A significant portion of the total time involved in completing a TEM sample with in-situ lift-out is spent during the holder-attach step. The relative amount of time involved depends on the amount of time required to mechanically isolate the lift-out sample from the initial bulk sample (ion beam milling rate), but will vary between 30% to 60% of the total time for TEM sample preparation. In order to eliminate the holder-attach step, it would be desirable to directly join the probe tip to the material that will form the TEM sample holder, and thereafter attach the excised sample to the probe tip of the newly-formed TEM sample holder. This newly created assembly is robust and easy to pick up with the tweezers, allowing smooth transfer inside and outside the FIB without the necessity to vent the FIB vacuum chamber.